Golf balls having a foam center with regions of different hardness

ABSTRACT

Golf balls having a multi-layered core made of a foamed composition are provided. The core preferably has a foam inner core (center) and surrounding thermoset or thermoplastic outer core layer. Preferably, a polyurethane foam composition is used to form the foam center. The foam inner core preferably includes a fully-foamed center region and a partially or completely-collapsed foam outer region. The hardness of the fully-foamed region is different than the hardness of the collapsed foam region. Non-foamed thermoset or thermoplastic materials such as polybutadiene rubbers or ethylene acid copolymer ionomer may be used to form the outer core layer. The ball further includes a cover that may be multi-layered. The foam cores have good resiliency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending, co-assigned, U.S.patent application Ser. No. 15/071,381 having a filing date of Mar. 16,2016, now allowed, the entire disclosure of which is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to multi-layered, golf ballshaving a foam core with regions of different hardness. A dual-layeredcore having an inner core (center) and surrounding thermoset orthermoplastic outer core layer is preferably prepared. The foam centerpreferably includes a fully-foamed region and a partially orcompletely-collapsed foam region. The hardness of the fully-foamedregion is different than the hardness of the collapsed foam region. Theball further includes a cover having at least one layer.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including, for example, ethylene acid copolymerionomers, polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable performance properties have contributed to thesemulti-piece balls becoming more popular. Many golf balls used today havemulti-layered cores comprising an inner core and at least onesurrounding outer core layer. For example, the inner core may be made ofa relatively soft and resilient material, while the outer core may bemade of a harder and more rigid material. The “dual-core” sub-assemblyis encapsulated by a cover having at least one layer to provide a finalball assembly. Different materials can be used to manufacture the coreand cover thus imparting desirable properties to the final ball.

In general, dual-cores comprising an inner core (or center) and asurrounding outer core layer are known in the industry. For example,Sugimoto, U.S. Pat. No. 6,390,935 discloses a three-piece golf ballcomprising a core having a center and outer shell and a cover disposedabout the core. The specific gravity of the outer shell is greater thanthe specific gravity of the center. The center has a JIS-C hardness (X)at the center point thereof and a JIS-C hardness (Y) at a surfacethereof satisfying the equation: (Y−X)≥8. The core structure (center andouter shell) has a JIS-C hardness (Z) at a surface of 80 or greater. Thecover has a Shore D hardness of less than 60.

Endo, U.S. Pat. No. 6,520,872 discloses a three-piece golf ballcomprising a center, an intermediate layer formed over the center, and acover formed over the intermediate layer. The center is preferably madeof high-cis polybutadiene rubber; and the intermediate and cover layersare preferably made of an ionomer resin such as an ethylene acidcopolymer.

Watanabe, U.S. Pat. No. 7,160,208 discloses a three-piece golf ballcomprising a rubber-based inner core; a rubber-based outer core layer;and a polyurethane elastomer-based cover. The inner core layer has aJIS-C hardness of 50 to 85; the outer core layer has a JIS-C hardness of70 to 90; and the cover has a Shore D hardness of 46 to 55. Also, theinner core has a specific gravity of more than 1.0, and the core outerlayer has a specific gravity equal to or greater than that of that ofthe inner core.

The core sub-structure located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance versusballs with low COR values. These properties are particularly importantfor long distance shots. For example, balls having high resiliency andCOR values tend to travel a relatively far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif the ball is hooked or sliced. Meanwhile, the “feel” of the ballgenerally refers to the sensation that a player experiences whenstriking the ball with the club and it is a difficult property toquantify. Most players prefer balls having a soft feel, because theplayer experience a more natural and comfortable sensation when theirclub face makes contact with these balls. Balls having a softer feel areparticularly desirable when making short shots around the green, becausethe player senses more with such balls. The feel of the ball primarilydepends upon the hardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials for improving the playing performance and other properties ofthe ball. For example, golf balls containing cores made from foamcompositions are generally known in the industry. Puckett and Cadorniga,U.S. Pat. Nos. 4,836,552 and 4,839,116 disclose one-piece, shortdistance golf balls made of a foam composition comprising athermoplastic polymer (ethylene acid copolymer ionomer such as Surlyn®)and filler material (microscopic glass bubbles). The density of thecomposition increases from the center to the surface of the ball. Thus,the ball has relatively dense outer skin and a cellular inner core.According to the '552 and '116 patents, by providing a short distancegolf ball, which will play approximately 50% of the distance of aconventional golf ball, the land requirements for a golf course can bereduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece golf ball(FIG. 2) containing a high density center (3) made of steel, surroundedby an outer core (4) of low density resilient syntactic foamcomposition, and encapsulated by an ethylene acid copolymer ionomer(Surlyn®) cover (5). The '126 patent defines the syntactic foam as beinga low density composition consisting of granulated cork or hollowspheres of either phenolic, epoxy, ceramic or glass, dispersed within aresilient elastomer.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprising an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.Alternatively, the compressible material may be dispersed throughout theentire core. In one embodiment, the core comprises an inner and outerportion. In another embodiment, the core comprises inner and outerlayers.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core, optional intermediate layer, andhigh specific gravity cover with Shore D hardness in the range of about40 to about 80. The core is preferably made from a highly neutralizedthermoplastic polymer such as ethylene acid copolymer which has beenfoamed.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

Although some foam core constructions for golf balls have beenconsidered over the years, there are drawbacks with using such foammaterials. For example, one disadvantage with golf balls having a foamcore is the ball tends to have low resiliency (rebounding performance).That is, the velocity of the ball tends to be low after being hit by aclub and the ball generally travels short distances. There is a need fornew balls having a foam core with improved resiliency that will allowplayers to generate higher initial ball speed. This will allow playersto make longer distance shots. The present invention provides new foamcore constructions having improved resiliency and durability and otheradvantageous properties; and new methods for making such cores. Theinvention also encompasses new golf balls containing the improved coreconstruction.

SUMMARY OF THE INVENTION

The present invention provides a golf ball comprising a core assemblyand cover. The golf ball comprises an inner core layer comprising a foamcomposition. The inner core generally has a diameter in the range ofabout 0.100 to about 1.100 inches, and preferably about 0.100 to about0.900 inches. The foamed inner core has a geometric center, outersurface region, and outer surface skin, wherein the foam composition isfoamed in the center and at least partially-collapsed in the outerregion. The foam may be completely collapsed in the outer region. Theinner core also has an outer surface hardness (H_(inner core surface))and a center hardness (H_(inner core center)), wherein theH_(inner core surface) is greater than the H_(inner core center) toprovide a positive hardness gradient in the inner core. The outer corelayer comprises a non-foamed thermoset or thermoplastic composition. Theouter core layer is disposed about the inner core and has a thickness inthe range of about 0.100 to about 0.750 inches, preferably about 0.250to about 0.650 inches. The outer surface hardness of the outer corelayer is preferably greater than the center hardness of the inner coreso as to provide a positive hardness gradient across the core assembly.

In one embodiment, the method for making the core assembly (foamed innercore and surrounding non-foamed outer core layer) comprises thefollowing steps. First, a foam composition is molded into an inner corestructure. Then, the foamed inner core structure is thermally orchemically-treated so as to at least partially-collapse the foam in theouter region. In some instances, the foam in the outer region iscompletely collapsed by this treatment.

The foamed inner core preferably has regions of different hardness. Forexample, in one version, the (H_(inner core center)) is preferably inthe range of about 10 to about 55 Shore C and the(H_(inner core surface)) is preferably in the range of about 15 to about60 Shore C to provide a positive hardness gradient across the innercore. The foamed inner core also may have a midpoint hardness in theouter region (H_(midpoint inner core outer region)), wherein theH_(inner core surface) is greater than theH_(midpoint inner core outer region) and theH_(midpoint inner core outer region) is greater than theH_(inner core center). Thus, in one instance, theH_(inner core surface)>H_(midpoint inner core outer region)>H_(inner core center).Also, the outer core layer may have an outer surface hardness(H_(outer surface of OC)) and a midpoint hardness (H_(midpoint of OC)),wherein the H_(outer surface of OC) is greater than theH_(midpoint of OC) to provide a positive hardness gradient across theouter core. For example, the H_(outer surface of OC) may be in the rangeof about 50 to about 98 Shore C and the H_(midpoint of OC) may be in therange of about 45 to about 90 Shore C to provide a positive hardnessgradient. In yet another version, the H_(outer surface of OC) is lessthan the H_(midpoint of OC) to provide a negative hardness gradient. Forexample, the H_(outer surface of OC) may be in the range of about 42 toabout 92 Shore C and the H_(midpoint of OC) may be in the range of about47 to about 97 Shore C.

The foamed inner core also preferably has regions of different density.For example, the foamed inner core may have an outer surface specificgravity (SG_(inner core surface)) and a center specific gravity(SG_(inner core center)), wherein the SG_(inner core surface) is greaterthan the SG_(inner core center). The foamed inner core also may have amidpoint specific gravity in the outer region (SG_(midpoint) inner coreouter region), wherein the SG_(inner core surface) is greater than theSG_(midpoint inner core outer region) and theSG_(midpoint inner core outer region) is greater than theSG_(inner core center). Thus, in one instance, theSG_(inner core surface)>SG_(midpoint inner core outer region)>SG_(inner core center).

Thermoset or thermoplastic materials are used to form the foamed innercore, and preferably a foamed polyurethane inner core is prepared.Non-foamed thermoset or thermoplastic materials also may be used to formthe outer core layer. Preferably, a thermoset rubber material such aspolybutadiene rubber is used. Thus, in one embodiment, the dual-coreincludes a foam inner core (center) and a surrounding non-foamedthermoset core layer that is preferably made from polybutadiene rubber.In another embodiment, the dual-core includes a foam inner core (center)and a surrounding non-foamed thermoplastic core layer made frompartially or highly neutralized olefin acid copolymers. Non-ionomericthermoplastic polymers also may be used.

The core layers preferably have different hardness gradients. Forexample, each core layer may have a positive, zero, or negative hardnessgradient as described above. In a first embodiment, the inner core has apositive hardness gradient; and the outer core layer has a positivehardness gradient. In yet another embodiment, the inner core has apositive hardness gradient, and the outer core layer has zero ornegative hardness gradient.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a is a cross-sectional view of a spherical inner core showinga foamed geometric center, outer region, and outer surface skin, theinner core being made in accordance with the present invention;

FIG. 1A is a is a cross-sectional view of a core assembly showing aninner core having a foamed geometric center, partially-collapsed foamedouter region, and outer surface skin; and a surrounding outer corelayer, the core assembly being made in accordance with the presentinvention;

FIG. 1B is a photomicrograph showing a cross-sectional view of a coreassembly with an inner core having a foamed geometric center,partially-collapsed foamed outer region, and outer surface skin; and asurrounding outer core layer, the core assembly being made in accordancewith the present invention;

FIG. 2 is a perspective view of one embodiment of upper and lower moldcavities used to make the inner core of the present invention;

FIG. 3 is a perspective view of a spherical inner core made of a foamedcomposition and two half-shells made of a thermoset rubber compositionin accordance with the present invention;

FIG. 3A is a perspective view of one embodiment of upper and lower moldcavities used to mold the outer core layer so that it encapsulates theinner core of FIG. 3 in accordance with the present invention;

FIG. 4 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 5 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention; and

FIG. 6 is a perspective view of a finished golf ball having a dimpledcover made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having two-piece, three-piece,four-piece, and five-piece constructions with single or multi-layeredcover materials may be made. Representative illustrations of such golfball constructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a three-piece golf ballcontaining a dual-layered core and single-layered cover is made. Thedual-core includes an inner core (center) and surrounding outer corelayer. In another version, a four-piece golf ball containing a dual-coreand dual-cover (inner cover and outer cover layers) is made. In yetanother construction, a four-piece or five-piece golf ball containing adual-core; casing layer(s); and cover layer(s) may be made. Two-piecegolf balls containing a center and surrounding cover also may be made.As used herein, the term, “casing layer” means a layer of the balldisposed between the multi-layered core sub-assembly and cover. Thecasing layer also may be referred to as a mantle or intermediate layer.The diameter and thickness of the different layers along with propertiessuch as hardness and compression may vary depending upon theconstruction and desired playing performance properties of the golfball.

Inner Core Composition

Preferably, the golf balls of this invention contain a core structurecomprising an inner core (center) and encapsulating outer core layer. Inthe present invention, a foam composition is used to make the innercore. The method for making the foamed inner core comprises thefollowing distinct steps. First, a foam composition is molded into aninner core structure. This molding process is described in furtherdetail below. Referring to FIG. 1, an inner core (4) is made from afoamed composition that includes a geometric center (6) and surroundingouter surface region (7) and outer surface (8). When the inner corestructure (4) is first made, the geometric center (6) and surroundingouter region (7) are foamed. The outer surface (8) of the inner core isgenerally a non-foamed, and relatively thin and dense layer. Thissurface may be referred to as the “skin” of the foamed composition. Inone embodiment, the thickness of the outer skin (8) is in the range ofabout 0.001 inches (1 mil) to about 0.500 inches (500 mils) andpreferably in the range of about 0.100 to about 0.300 inches. Morepreferably, the thickness of the outer skin (8) is preferably less thanabout 0.250 inches and even more preferably less than 0.150 inches.

In a subsequent step, as described in further detail below, the foamedinner core (4) is thermally or chemically-treated. For example, in onepreferred embodiment, an outer core layer is over-molded the inner corestructure. In this process, the heat used in the molding cycleactivates/decomposes the foamed outer region (7) of the inner core (4).This over-molding step causes the foamed outer region (7) of the innercore (4) to at least partially collapse. Referring to FIG. 1A, the innercore (4 a) is shown with a foamed geometric center (6 a) andpartially-collapsed outer region (7 a) and outer surface (skin) (8 a).An outer core (5), which is formed by this over-molding process,surrounds the inner core (4 a). In some instances, the foam in the outerregion (7 a) is completely collapsed by this treatment. Meanwhile, thefoamed state of the geometric enter (6 a) is maintained. In FIG. 1B, aphotomicrograph shows the inner core with a foamed geometric center,partially-collapsed outer region, and an outer skin, wherein thedifferent morphologies of the regions are visible. For example, thereare less foam cells visible in the partially-collapsed outer region. Anouter core (5), which is formed by this over-molding process, surroundsthe inner core (4 a). The outer core layer (5) may be molded over thefoamed inner core (4 a) using a variety of molding methods that involvesubjecting the inner core (4 a) to heat and pressure as described infurther detail below. This treatment creates a non-foamed outer region(7 a) having different properties than the foamed center of the innercore (4 a). For example, in one preferred embodiment, the hardness ofthe outer region (7 a) is greater than the hardness of the center (6 a)to create a positive hardness gradient across the inner core structure(4). These hardness gradients are discussed in further detail below. Thespecific gravity or density) of the outer region (7 a) also may begreater than the specific gravity of the center (6 a). Other thermal andchemical treatments for partially or completely collapsing the foam inthe outer region (7) are described further below. For example, inanother version, an over-molding process is not used. Rather, the foamedinner core structure (4) may be placed by itself in a slightly smallermold than originally used to make the structure, and heat/pressure maybe applied so the foam in the outer region (7) partially orcompletely-collapses.

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition having either an openor closed cellular structure. Flexible foams generally have an open cellstructure, where the cells walls are incomplete and contain small holesthrough which liquid and air can permeate. Rigid foams generally have aclosed cell structure, where the cell walls are continuous and complete.Many foams contain both open and closed cells. It also is possible toformulate flexible foams having a closed cell structure and likewise toformulate rigid foams having an open cell structure. Variousthermoplastic and thermoset materials may be used in forming the foamcompositions of this invention as discussed further below. In onepreferred embodiment, a polyurethane foam composition is prepared.

The foaming (blowing) agents used to form the foam are typically are inthe form of powder, pellets, or liquids and they are added to thecomposition, where they decompose or react during heating and generategaseous by-products (for example, nitrogen or carbon dioxide). The gasis dispersed and trapped throughout the composition and foams it. Forexample, water may be used as the foaming agent. Air bubbles areintroduced into the mixture of the isocyanate and polyol compounds andwater by high-speed mixing equipment. As discussed in more detailfurther below, the isocyanates react with the water to generate carbondioxide which fills and expands the cells created during the mixingprocess.

The chemical foaming agents may be inorganic, such as ammonium carbonateand carbonates of alkalai metals, or may be organic, such as azo anddiazo compounds, such as nitrogen-based azo compounds. Suitable azocompounds include, but are not limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), and azodicarbonamide. Other compoundsinclude, for example, p,p′-oxybis(benzene sulfonyl hydrazide), p-toluenesulfonyl semicarbazide, and p-toluene sulfonyl hydrazide. Other foamingagents include any of the Celogens® sold by Crompton ChemicalCorporation, and nitroso compounds, sulfonylhydrazides, azides oforganic acids and their analogs, triazines, tri- and tetrazolederivatives, sulfonyl semicarbazides, urea derivatives, guanidinederivatives, and esters such as alkoxyboroxines. Also, foaming agentsthat liberate gasses as a result of chemical interaction betweencomponents such as mixtures of acids and metals, mixtures of organicacids and inorganic carbonates, mixtures of nitriles and ammonium salts,and the hydrolytic decomposition of urea may be used. In the presentinvention, the foam composition preferably is formed from chemicalblowing agents.

Chemical Blowing Agents.

One or more chemical blowing agents are added to the formulation thatwill be foamed. Water is a preferred blowing agent. When added to thepolyurethane formulation, water will react with the isocyanate groupsand form carbamic acid intermediates. The carbamic acids readilydecarboxylate to form an amine and carbon dioxide. The newly formedamine can then further react with other isocyanate groups to form urealinkages and the carbon dioxide forms the bubbles to produce the foam.The water is added in a sufficient amount to cause the mixture to foam.In one preferred embodiment, the water is present in the composition inan amount in the range of 0.25 to 3.0% by weight based on total weightof the composition.

Physical Blowing Agents.

The physical blowing agents are different materials and have differentworking mechanisms than the chemical blowing agents. The physicalblowing agents may be used, in addition to or as an alternative to, thechemical blowing agents. These blowing agents typically are gasses thatare introduced under high pressure directly into the polymercomposition. Chlorofluorocarbons (CFCs) and partially halogenatedchlorofluorocarbons are effective, but these compounds are banned inmany countries because of their environmental side effects.Alternatively, aliphatic and cyclic hydrocarbon gasses such as isobuteneand pentane may be used. Inert gasses, such as carbon dioxide andnitrogen, also are suitable. With physical blowing agents, theisocyanate and polyol compounds react to form polyurethane linkages andthe reaction generates heat. Foam cells are generated and as the foamingagent vaporizes, the gas becomes trapped in the cells of the foam.

Other suitable blowing agents may be selected, for example, from thegroup consisting of azo compounds such as azodicarbonamide (ADCA) andazobisformamide; nitroso compounds such as N, N-dimethyl-N, N-dinitrosoterephthalamide, N, N-dinitroso-pentamethylene-tetramine (DPT), and5-Phenyltetrazole (5 PT); hydrazine derivatives such as 4,4′-Oxybis(benzenesulfonylhydrazide) (OBSH), hydrazodicarbonamide (HDCA),toluenesulfonyl hydrazide (TSH), and benzene-sulfonyl-hydrazide (BSH),carbazide compounds such as toluenesulfonyl-semicarbazide (TSH); andhydrogen carbonates such as sodium hydrogen carbonate (NaHCO₃); andmixtures thereof. In one preferred embodiment, chemical blowing agentshaving relatively low decomposition temperatures that complement theheating temperatures in the molding cycle are used. These blowing agentswill start to decompose as the designated temperature in the moldingprocess, and the foaming reaction will proceed more quickly. Forexample, the blowing agent may be selected from the group consisting ofOBSH, having a decomposition temperature of about 160° C. and NaHCO₃having a decomposition temperature of about 150° C. These blowing agentsare commercially available from such companies as Tramaco, GmbH(Pinneberg, Germany) and Eiwa Chemical Ind. Co., Ltd. (Mitsubishi GasChemical America, Inc., Detroit, Mich.).

It is recognized that during the decomposition reaction of certainchemical foaming agents, more heat and energy is released than is neededfor the reaction. Once the decomposition has started, it continues for arelatively long time period. If these foaming agents are used, longercooling periods are generally required. Hydrazide and azo-basedcompounds often are used as exothermic foaming agents. On the otherhand, endothermic foaming agents need energy for decomposition. Thus,the release of the gasses quickly stops after the supply of heat to thecomposition has been terminated. If the composition is produced usingthese foaming agents, shorter cooling periods are needed. Bicarbonateand citric acid-based foaming agents can be used as exothermic foamingagents.

Additional Blowing Agents.

Other suitable blowing agents that may be added to the formulation thatwill be foamed in accordance with this invention include, for example,expandable gas-containing microspheres. Exemplary microspheres consistof an acrylonitrile polymer shell encapsulating a volatile gas, such asisopentane gas. This gas is contained within the sphere as a blowingagent. In their unexpanded state, the diameter of these hollow spheresrange from 10 to 17 μm and have a true density of 1000 to 1300 kg/m³.When heated, the gas inside the shell increases its pressure and thethermoplastic shell softens, resulting in a dramatic increase of thevolume of the microspheres. Fully expanded, the volume of themicrospheres will increase more than 40 times (typical diameter valueswould be an increase from 10 to 40 μm), resulting in a true densitybelow 30 kg/m³ (0.25 lbs/gallon). Typical expansion temperatures rangefrom 80-190° C. (176-374° F.). Such expandable microspheres arecommercially available as Expancel® from Expancel of Sweden or AkzoNobel.

In the process of this invention, the materials used to prepare the foamare charged to the mold for producing the inner core. The mold may beequipped with steam nozzles so that steam can be injected into the moldcavity. The temperature inside of the mold can vary, for example, thetemperature can range from about 80° C. to about 400° C. Steam, hot air,hot water, or radiant heat may be used to foam the composition. Thecomposition expands as it is heated. The temperature must be chosencarefully and must be sufficiently high so that it activates the blowingagents and foams the mixture, but it must not be excessively high. Ingeneral, the temperature should be in the range of about roomtemperature (RT) to about 180° F. and preferably in the range of aboutroom temperature (RT) to about 150° F. so that it activates the blowingagents. Once the polymer materials, blowing agents, and any optionalingredients (for example, fillers) are charged to the mold and treatedwith sufficient heat and pressure, the blowing agents are activated.This causes the polymer mixture to foam and generate the foamcomposition in the mold.

Foam Polymers.

As discussed above, polyurethane foam is preferably prepared inaccordance with this invention. It is recognized, however, that a widevariety of thermoplastic and thermoset materials may be used in formingthe foam compositions of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylicacid copolymers, commercially available from Dow Chemical Company; andClarix® ionomer resins, commercially available from A. Schulman Inc.);polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof.

Castable polyurethanes, polyureas, and hybrids ofpolyurethanes-polyureas are particularly desirable because thesematerials can be used to make a golf ball having good playingperformance properties as discussed further below. By the term, “hybridsof polyurethane and polyurea,” it is meant to include copolymers andblends thereof. Basically, polyurethane compositions contain urethanelinkages formed by the reaction of a multi-functional isocyanatecontaining two or more NCO groups with a polyol having two or morehydroxyl groups (OH—OH) sometimes in the presence of a catalyst andother additives. Generally, polyurethanes can be produced in asingle-step reaction (one-shot) or in a two-step reaction via aprepolymer or quasi-prepolymer. In the one-shot method, all of thecomponents are combined at once, that is, all of the raw ingredients areadded to a reaction vessel, and the reaction is allowed to take place.In the prepolymer method, an excess of polyisocyanate is first reactedwith some amount of a polyol to form the prepolymer which containsreactive NCO groups. This prepolymer is then reacted again with a chainextender or curing agent polyol to form the final polyurethane. Polyureacompositions, which are distinct from the above-described polyurethanes,also can be formed. In general, polyurea compositions contain urealinkages formed by reacting an isocyanate group (—N═C═O) with an aminegroup (NH or NH₂). Polyureas can be produced in similar fashion topolyurethanes by either a one shot or prepolymer method. In forming apolyurea polymer, the polyol would be substituted with a suitablepolyamine. Hybrid compositions containing urethane and urea linkagesalso may be produced. For example, when polyurethane prepolymer isreacted with amine-terminated curing agents during the chain-extendingstep, any excess isocyanate groups in the prepolymer will react with theamine groups in the curing agent. The resulting polyurethane-ureacomposition contains urethane and urea linkages and may be referred toas a hybrid. In another example, a hybrid composition may be producedwhen a polyurea prepolymer is reacted with a hydroxyl-terminated curingagent. A wide variety of isocyanates, polyols, polyamines, and curingagents can be used to form the polyurethane and polyurea compositions asdiscussed further below.

More particularly, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediol such, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines, 3,3′,5,5‘-tetraethyl-4,4’-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, fillers,cross-linking agents, chain extenders, surfactants, dyes and pigments,coloring agents, fluorescent agents, adsorbents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Fillers.

The foam composition may contain fillers such as, for example, mineralfiller particulate. Suitable mineral filler particulates includecompounds such as zinc oxide, limestone, silica, mica, barytes,lithopone, zinc sulfide, talc, calcium carbonate, magnesium carbonate,clays, powdered metals and alloys such as bismuth, brass, bronze,cobalt, copper, iron, nickel, tungsten, aluminum, tin, precipitatedhydrated silica, fumed silica, mica, calcium metasilicate, bariumsulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, carbonates such as calcium or magnesium or bariumcarbonate, sulfates such as calcium or magnesium or barium sulfate.Silicon dioxides are particularly preferred because they are based onSi—O bonds and these material are compatible with the Si—O—Si backboneof the silicone foam. Adding fillers to the composition provides manybenefits including helping improve the stiffness and strength of thecomposition. The mineral fillers tend to help decrease the size of thefoam cells and increase cell density. The mineral fillers also tend tohelp improve the physical properties of the foam such as hardness,compression set, and tensile strength.

More particularly, clay particulate fillers, such as Garamite® mixedmineral thixotropes and Cloisite® and Nanofil® nanoclays, commerciallyavailable from Southern Clay Products, Inc., and Nanomax® and Nanomer®nanoclays, commercially available from Nanocor, Inc may be used. Othernano-scale materials such as nanotubes and nanoflakes also may be used.Also, talc particulate (e.g., Luzenac HAR® high aspect ratio talcs,commercially available from Luzenac America, Inc.), glass (e.g., glassflake, milled glass, and microglass), and combinations thereof may beused. Metal oxide fillers have good heat-stability and include, forexample, aluminum oxide, zinc oxide, tin oxide, barium sulfate, zincsulfate, calcium oxide, calcium carbonate, zinc carbonate, bariumcarbonate, tungsten, tungsten carbide, and lead silicate fillers. Thesemetal oxides and other metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof may be added to the silicone foam composition.

As discussed further below, in one preferred embodiment, the specificgravity (or density) of the foam inner core is less than the specificgravity of the outer core. In this embodiment, if an excess amount ofmineral filler or other additives are included in the foam composition,they should not be added in an amount that would increase the specificgravity (or density) of the foam inner core to a level such that itwould be greater than the specific gravity of the outer core layer. Ifthe ball's mass is concentrated towards the outer surface (for example,outer core layers), and the outer core layer has a higher specificgravity than the inner core, the ball has a relatively high Moment ofInertia (MOI). In such balls, most of the mass is located away from theball's axis of rotation and thus more force is needed to generate spin.These balls have a generally low spin rate as the ball leaves the club'sface after contact between the ball and club. Such core structures(wherein the specific gravity of the outer core is greater than thespecific gravity of the inner core) are preferred in the presentinvention. Thus, in one preferred embodiment, the concentration ofmineral filler particulate in the foam composition is in the range ofabout 0.1 to about 9.0% by weight.

Molding of Outer Core Over the Inner Core

As discussed above, the inner core (center) is made preferably from afoamed polyurethane composition. Preferably, a two-layered or dual-coreis made, wherein the inner core is surrounded by an outer core layer. Inone preferred embodiment, the outer core layer is formed from anon-foamed thermoset composition and more preferably from a non-foamedthermoset rubber composition.

In the present invention, the inner core (center) of the golf ballcomprises a foam thermoplastic or thermoset polymer composition that maybe prepared using the above-described methods. Preferably, the centercomprises a polyurethane foam composition. The foam may have an open orclosed cellular structure or combinations thereof and may range fromrelatively rigid foam to very flexible foam. Referring back to FIG. 1, afoamed inner core (4) having a geometric center (6), surrounding outerregion (7), and outer surface skin (8) is shown. The foamed inner corestructure (4) may be produced using the molding methods describedfurther below.

Referring to FIG. 2, one version of a mold for preparing the foamedinner core is shown. The mold includes lower and upper mold cavities (9,10) that are placed in lower and upper mold frame plates (11, 12). Theframe plates (11, 12) contain guide pins and complementary alignmentholes (not shown in drawing). The guide pins are inserted into thealignment holes to secure the lower plate (11) to the upper plate (12).The lower and upper mold cavities (9, 10) are mated together as theframe plates (11, 12) are fastened. When the lower and upper moldcavities (9, 10) are joined together, they define an interior sphericalcavity that houses the spherical core. The upper mold contains a vent orhole (14) to allow for the expanding foam to fill the cavitiesuniformly. A secondary overflow chamber (16), which is located above thevent (14), can be used to adjust the amount of foam overflow and thusadjust the density of the core structure being molded in the cavities.As the lower and upper mold cavities (9, 10) are mated together andsufficient heat and pressure is applied, the reactants of the foamcomposition react, cure, and solidify to form a relatively rigid orflexible and lightweight spherical foam core. The resulting cores arecooled and then removed from the mold.

The materials used to prepare the foam are charged to the mold forproducing the inner core. The mold may be equipped with steam nozzles sothat steam can be injected into the mold cavity. The temperature insideof the mold can vary, for example, the temperature can range from about80° C. to about 400° C. Steam, hot air, hot water, or radiant heat maybe used to foam the composition. The composition expands as it isheated. The temperature must be chosen carefully and must besufficiently high so that it activates the blowing agents and foams themixture. In general, the temperature should be in the range of about 80°C. to about 250° C. and preferably in the range of about 90° C. to about220° C. so that it activates the blowing agents.

Once the polymer materials, blowing agent, and any optional ingredients(for example, fillers) are charged to the mold and treated withsufficient heat and pressure, the blowing agents are activated. Water isa preferred chemical blowing agent. When added to the polyurethaneformulation that will be foamed, water will react with the isocyanategroups and form carbamic acid intermediates. The carbamic acids readilydecarboxylate to form an amine and carbon dioxide. The newly formedamine can then further react with other isocyanate groups to form urealinkages and the carbon dioxide forms the bubbles to produce the foam.

As discussed above, the inner core structure (4) that is molded from afoam composition includes foamed geometric center and outer regions (6,7) and a non-foamed outer skin (8). In practice, the reactants forproducing the foamed composition are added to a spherical mold. As thereaction progresses, the foaming material starts to generate carbondioxide gas that will fill the foam cells. This gas is trapped insidethe polymer cellular network and expands the foaming material. Once theexpanding foamed article hits the walls of the mold cavity, the foamcannot expand anymore due to the physical constraints of the cavity.This physical constraint causes a higher density region at the interfaceof the cavity, while the center of the foamed article remains at a lowerdensity with more dispersed gas bubbles. There is also a temperaturedifference between the outer surface of the foamed article that hits thecavity walls and center of the foamed article. As a result of thistemperature difference, less carbon dioxide gas for filling the cells isgenerated at the outer region than the center region of the foamingmaterial. Thus, a non-foamed, relatively dense skin layer is formed onthe outer surface of the foamed article. Vents may be added to thespherical mold of various sizes and shapes so that more or less pressuremay be built up in the cavity and the thickness of the outer skin layercan be tailored.

In a second step, the foamed inner core (4) is treated thermally orchemically to at least partially-collapse the foam in the outer region(7). For example, in an over-molding process, the outer core layer (5)is prepared by molding the outer core composition over the inner core(4). The outer core layer (5) may be molded over the foamed inner core(4) using a variety of molding techniques. Suitable thermoset andthermoplastic materials that may be used to form the outer core layerare described further below.

For example, the outer core composition (preferably a thermoset rubbercomposition) may be injection-molded or compression-molded to producehalf-shells. These smooth-surfaced or textured hemispherical shells arethen placed around the foamed, spherical inner core in a compressionmold. Under sufficient heating and pressure, the shells fuse together toform an outer core layer that encapsulates the foamed inner core. Moreparticularly, as shown in FIGS. 3 and 3A, after the two half-shells (17a 17 b) made from a rubber or other composition have been prepared, theyare joined together in a mold to encase the previously molded inner core(4). The hemispherical shells (17 a, 17 b) and inner core (4) are placedin a mold between a first mold member (17 a) and a second mold member(17 b). The first and second mold members (19, 19) are subsequentlypressed together to join together the half-shells (17 a, 17 b) undersufficient heat and pressure. This molding process forms the outer corelayer. As a result, a finished core assembly (inner core and surroundingouter core layer) is produced.

In another method, the outer core composition may be added to aninjection-molding machine. After the foamed inner core has beenpositioned properly in the injection-molding cavity, the outer corecomposition is injection-molded directly over the inner core.

Referring back to FIGS. 1 and 1A, during over-molding of the foamedinner core (4) center with the outer core layer composition (5), theheat used in the molding cycle activates/decomposes the foamed outerregion (7) of the inner core. This step causes the outer region (7) toat least partially collapse. In turn, the partially-collapsed foamedouter region (7) becomes at least partially non-foamed. The outer region(7) becomes more solid and dense (that is, less foamed). In someinstances, the foamed outer region (7) collapses completely and becomescompletely non-foamed. The properties of the different inner coreregions may change. For example, in one preferred embodiment, thehardness of the partially or completely foam-collapsed outer region (7a) becomes greater than the hardness of the foamed center (6 a) tocreate a positive hardness gradient across the inner core structure (4a). The outer skin (8 a) of the foamed inner core (4 a) also hashardness. These hardness gradients are discussed in further detailbelow. The outer core layer (5), which is formed during the over-moldingstep, encapsulates the foamed inner core (4 a).

As discussed above, a dual-layered core assembly comprising an innercore (4 a) and outer core layer (5) is formed in accordance with thisinvention. The core assembly is used to manufacture a finished golfball. For example, referring to FIG. 4, in one version, a four-piecegolf ball generally indicated at (20) can be made in accordance withthis invention. The ball (20) contains an inner core (center) (22) andsurrounding outer core layer (24). The dual-core sub-assembly is encasedby a multi-layered cover comprising an inner cover (26) and outer cover(28). Referring to FIG. 5, in another version, a three-piece golf ball(30) contains an inner core (center) (32) and outer core layer (34). Thedual-core sub-assembly is surrounded by a single-layered cover (36).

In an alternative process, the inner core may be chemically or thermallytreated in a separate step. For example, a fully-cured foamed inner coresphere may be put into the same sized mold as that sized mold originallyused to make the inner core sphere. Then, the inner core in the mold maybe exposed to heat such that the outer surface of the foamed compositionpartially-melts and collapses to form an outer region with a greaterdensity that that of the geometric center region. In yet another method,the mold could be slightly smaller than the original mold and thefully-cured foamed sphere may be exposed to heat, pressure, or both inorder to create the partially-collapsed outer region of greater density.A chemical-treatment may also be used to form an outer region of greaterdensity. For example, the foamed sphere may be exposed to a solvent thatpartially dissolves or softens the outer portion of the sphere in orderto cause it to collapse slightly. It is also possible to treat thefoamed sphere with a reactive mixture such as polyurethane, polyurea,epoxy, or other reactive polymer system. The liquid, non-reacted mixturecan fill the voids of the outer portion of the foamed sphere and reactto form a solid material. In this manner, the density of the outerportion of the foamed sphere can be increased.

Properties of Foams

The foam compositions of this invention have numerous chemical andphysical properties making them suitable for core assemblies in golfballs.

The density of the foam is an important property and is defines as theweight per unit volume (typically, g/cm³) and can be measured per ASTMD-1622. The hardness, stiffness, and load-bearing capacity of the foamare independent of the foam's density, although foams having a highdensity typically have high hardness and stiffness. Normally, foamshaving higher densities have higher compression strength. Surprisingly,the foam compositions used to produce the inner core of the golf ballsper this invention have a relatively low density; however, the foams arenot necessarily soft and flexible, rather, they may be relatively firm,rigid, or semi-rigid depending upon the desired golf ball properties.Tensile strength, tear-resistance, and elongation generally refer to thefoam's ability to resist breaking or tearing, and these properties canbe measured per ASTM D-1623. The durability of foams is important,because introducing fillers and other additives into the foamcomposition can increase the tendency of the foam to break or tearapart. In general, the tensile strength of the foam compositions of thisinvention is in the range of about 20 to about 1000 psi (parallel to thefoam rise) and about 50 to about 1000 psi (perpendicular to the foamrise) as measured per ASTM D-1623 at 23° C. and 50% relative humidity(RH). Meanwhile, the flex modulus of the foams of this invention isgenerally in the range of about 5 to about 45 kPa as measured per ASTMD-790, and the foams generally have a compressive modulus of 200 to50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required to compress theblock by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

Hardness of the Inner Core

As shown in FIGS. 1-1B, a foamed inner core (4 a) having a foamedgeometric center (6 a) and outer skin (8 a) and a surrounding outer corelayer (5) may be prepared per the molding method discussed above. Thefoamed inner core (4 a) also includes a partially or completelynon-foamed outer region (7 a) that acts as a transition zone between thefoamed center (6 a) and outer skin (8 a).

The inner core preferably has a diameter within a range of about 0.150to about 1.120 inches. For example, the inner core may have a diameterwithin a range of about 0.300 to about 1.000 inches. In another example,the inner core may have a diameter within a range of about 0.500 toabout 0.800 inches. More particularly, the inner core preferably has adiameter size with a lower limit of about 0.15 or 0.17 or 0.25 or 0.30or 0.35 or 0.38 or 0.45 or 0.50 or 0.52 or 0.55 inches and an upperlimit of about 0.60 or 0.63 or 0.65 or 0.70 or 0.74 or 0.80 or 0.86 or0.90 or 0.95 or 1.00 or 1.02 or 1.08 or 1.12 inches. In FIG. 1A, thefoamed inner core (4 a) includes a geometric center (6 a), surroundingouter region (7 a), and outer skin surface (8 a). The thickness of thesurrounding outer region (7 a) is preferably in the range of about 0.010inches (10 mils) to about 0.550 inches (550 mils). In one preferredembodiment, the thickness of outer region (7 a) is preferably in therange of about 0.020 to about 0.440 inches and more preferably in therange of about 0.030 to about 0.250 inches.

In one preferred embodiment, the foamed core has a “positive” hardnessgradient (that is, the outer skin of the inner core is harder than itsgeometric center.) For example, the geometric center hardness of theinner core (H_(inner core center)), as measured in Shore C units, may beabout 10 Shore C or greater and preferably has a lower limit of about 10or 13 or 16 or 20 or 25 or 30 or 32 or 34 or 36 or 40 Shore C and anupper limit of about 42 or 44 or 48 or 50 or 52 or 56 or 60 or 62 or 65or 68 or 70 or 74 or 78 or 80 or 84 or 90 Shore C. In one preferredversion, the R_(inner core center) of the foamed inner core is about 40Shore C.

When a flexible, relatively soft foam is used, the geometric centerhardness of the inner core (H_(inner core center)) of the foam may havea Shore A hardness of about 10 or greater, and preferably has a lowerlimit of 15, 18, 20, 25, 28, 30, 35, 38, or 40 Shore A hardness and anupper limit of about 45 or 48, or 50, 54, 58, 60, 65, 70, 80, 85, or 90Shore A hardness. In one preferred embodiment, the H_(inner core center)of the foamed inner core is about 55 Shore A.

The R_(inner core center), as measured in Shore D units, is about 5Shore D or greater and more preferably within a range having a lowerlimit of about 5 or 8 or 12 or 15 or 18 or 20 or 22 or 25 or 28 or 30 or32 or 36 or 40 or 44 Shore D and an upper limit of about 45 or 48 or 50or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 72 or 74 or 78 or 80or 82 or 84 or 88 or 90 Shore D.

Meanwhile, the hardness of the outer region of the inner core(H_(midpoint of inner core outer region)) also may be measured. Thehardness of the midpoint of the outer region(H_(midpoint of inner core outer region)) may be taken at a pointequidistant from the geometric center and outer surface skin. TheH_(midpoint of inner core outer region), as measured in Shore C, ispreferably about 12 Shore C or greater and may have, for example, alower limit of about 12 or 15 or 18 or 20 or 22 or 24 or 28 or 30 or 32or 35 or 36 or 40 or 42 or 44 or 48 or 50 Shore C and an upper limit ofabout 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or86 or 88 or 90 or 92 or 95 Shore C. When a flexible, relatively softfoam is used, the H_(midpoint of inner core outer region) of the foammay have a Shore A hardness of about 10 or greater, and preferably has alower limit of 10, 12 15, 16, 20, 24, 26, 28, 30, 34, 40, 42, 46, or 50Shore A hardness and an upper limit of about 52, 55, 58, 60, 62, 66, 70,74, 78, 80, 84, 88, 90, or 95 Shore A hardness. In one preferredembodiment, the H_(midpoint of inner core outer region) is about 60Shore A. The H_(midpoint of inner core outer region), as measured inShore D units, preferably has a lower limit of about 10 or 12 or 16 or22 or 28 or 30 or 32 or 36 or 40 or 44 Shore D and an upper limit ofabout 45 or 48 or 50 or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or74 or 78 or 80 or 82 or 84 or 88 or 90 or 94 or 96 Shore D.

Also, the hardness of the outer skin surface of the inner core(H_(inner core surface)), as measured in Shore C, is preferably about 25Shore C or greater and may have, for example, a lower limit of about 25or 27 or 31 or 33 or 35 or 38 or 41 or 43 or 44 or 47 or 50 Shore C andan upper limit of about 55 or 61 or 63 or 65 or 73 or 77 or 80 or 82 or83 or 93 or 95 or 98 Shore C. When a flexible, relatively soft foam isused, the H_(inner core surface) of the foam may have a Shore A hardnessof about 18 or greater, and preferably has a lower limit of 18, 20, 27,29, 30, 33, 40, 45, or 50 Shore A hardness and an upper limit of about55, 58, 61, 66, 70, 77, 80, 84, 87, 93, or 95 Shore A hardness. In onepreferred embodiment, the H_(inner core surface) is about 65 Shore A.The H_(inner core surface), as measured in Shore D units, preferably hasa lower limit of about 28 or 30 or 32 or 36 or 40 or 44 Shore D and anupper limit of about 45 or 48 or 50 or 52 or 55 or 61 or 65 or 70 or 73or 80 or 83 or 88 or 90 or 93 Shore D.

In one preferred embodiment, the foamed inner core has a midpointhardness in the outer region (H_(midpoint inner core outer region)),wherein the H_(inner core surface) is greater than theH_(midpoint inner core outer region) and theH_(midpoint inner core outer region) is greater than theH_(inner core center). Thus, in one instance, theH_(inner core surface)>H_(midpoint inner core outer region)>H_(inner core center).

Density of the Inner Core

The foamed inner core preferably has a specific gravity of about 0.20 toabout 1.50 g/cc. That is, the density of the inner core (as measured atany point of the inner core structure) is preferably within the range ofabout 0.20 to about 1.50 g/cc. By the term, “specific gravity of theinner core” (“SG_(inner)”), it is generally meant the specific gravityof the inner core as measured at any point of the inner core structure.It should be understood, however, that the specific gravity values, astaken at different particular points of the inner core structure, mayvary. For example, the foamed inner core may have a “positive” densitygradient (that is, the outer surface (skin) of the inner core may have adensity greater than the geometric center of the inner core.) In onepreferred version, the specific gravity of the geometric center of theinner core (SG_(center of inner core)) is less than 0.80 g/cc and morepreferably less than 0.70 g/cc. More particularly, in one version, the(SG_(center of inner core)) is in the range of about 0.10 to about 0.06g/cc. For example, the (SG_(center of inner core)) may be within a rangehaving a lower limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.30 or0.35 or 0.37 or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and an upper limitof about 0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or 0.82 or 0.84or 0.85 or 0.88 or 0.90 g/cc.

Meanwhile, the specific gravity of the outer surface (skin) of the innercore (SG_(skin of inner core)), in one preferred version, is greaterthan about 0.90 g/cc and more preferably greater than 1.00 g/cc. Forexample, the (SG_(skin of inner core)) may fall within the range ofabout 0.90 to about 1.25 g/cc. More particularly, in one version, the(SG_(skin of inner core)) may have a specific gravity with a lower limitof about 0.90 or 0.92 or 0.95 or 0.98 or 1.00 or 1.02 or 1.06 or 1.10g/cc and an upper limit of about 1.12 or 1.15 or 1.18 or 1.20 or 1.24 or1.30 or 1.32 or 1.35 g/cc. In other instances, the outer skin may have aspecific gravity of less than 0.90 g/cc. For example, the specificgravity of the outer skin (SG_(skin of inner core)) may be about 0.75 or0.80 or 0.82 or 0.85 or 0.88 g/cc. In such instances, wherein both the(SG_(center of inner core)) and (SG_(skin of inner core)) are less than0.90 g/cc, it is still preferred that the (SG_(center of inner core)) beless than the (SG_(skin of inner core)).

As discussed above, the foamed inner core may have an outer surfacespecific gravity (SG_(inner core surface)) and a center specific gravity(SG_(inner core center)), wherein the SG_(inner core surface) is greaterthan the SG_(inner core center). In one preferred embodiment, the foamedinner core has a midpoint specific gravity in the outer region(SG_(midpoint inner core outer region)), wherein the SG_(inner core)surface is greater than the SG_(midpoint inner core outer region) andthe SG_(midpoint inner core outer region) is greater than theSG_(inner core center). Thus, in one instance, theSG_(inner core surface)>SG_(midpoint inner core outer region)>SG_(inner core center).

Thermoset Materials

As discussed above, the inner core (center) is made preferably from afoamed polyurethane composition. Preferably, a two-layered or dual-coreis made, wherein the inner core is surrounded by an outer core layer. Inone preferred embodiment, the outer core layer is formed from anon-foamed thermoset composition and more preferably from a non-foamedthermoset rubber composition.

Suitable thermoset rubber materials that may be used to form the outercore layer include, but are not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber composition also may include filler(s) such as materialsselected from carbon black, clay and nanoclay particles as discussedabove, talc (e.g., Luzenac HAR® high aspect ratio talcs, commerciallyavailable from Luzenac America, Inc.), glass (e.g., glass flake, milledglass, and microglass), mica and mica-based pigments (e.g., Iriodin®pearl luster pigments, commercially available from The Merck Group), andcombinations thereof. Metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed. As discussedfurther below, in one preferred embodiment, the specific gravity of theinner core layer (for example, foamed polyurethane) has a specificgravity less than the outer core layer (for example, polybutadienerubber). In such an event, if mineral, metal, or other fillers are addedto the polybutadiene rubber composition used to form the outer core, itis important the concentration of such fillers be sufficient so that thespecific gravity of the outer core layer is greater than the specificgravity of the inner core. For example, the concentration of the fillersmay be in an amount of at least about 5% by weight based on total weightof composition

In addition, the rubber compositions may include antioxidants. Also,processing aids such as high molecular weight organic acids and saltsthereof may be added to the composition. Suitable organic acids arealiphatic organic acids, aromatic organic acids, saturatedmono-functional organic acids, unsaturated monofunctional organic acids,multi-unsaturated mono-functional organic acids, and dimerizedderivatives thereof. Particular examples of suitable organic acidsinclude, but are not limited to, caproic acid, caprylic acid, capricacid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid,linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylaceticacid, naphthalenoic acid, and dimerized derivatives thereof. The organicacids are aliphatic, mono-functional (saturated, unsaturated, ormulti-unsaturated) organic acids. Salts of these organic acids may alsobe employed. The salts of organic acids include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending.) Otheringredients such as accelerators (for example, tetra methylthiuram),processing aids, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, chemical blowing andfoaming agents, defoaming agents, stabilizers, softening agents, impactmodifiers, antiozonants, as well as other additives known in the art maybe added to the rubber composition.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; and DIENE 55NF, 70AC, and 320 AC, availablefrom Firestone Polymers of Akron, Ohio.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

Thermoplastic Materials

As discussed above, in one preferred embodiment, a thermoset rubbercomposition is used to form the outer core. In alternative embodiments,the outer core layer is made from a thermoplastic material, which ispreferably non-foamed, for example, a non-foamed ionomer composition.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers,wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturatedcarboxylic acid, and Y is a softening monomer. O is preferably selectedfrom ethylene and propylene. X is preferably selected from methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α,β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α,β-ethylenically unsaturated mono- ordicarboxylic acid in the acid copolymer is typically from 1 wt. % to 35wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %, basedon total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed in U.S.Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference. The acid copolymer can be reacted withthe optional high molecular weight organic acid and the cation sourcesimultaneously, or prior to the addition of the cation source. Suitablecation sources include, but are not limited to, metal ion sources, suchas compounds of alkali metals, alkaline earth metals, transition metals,and rare earth elements; ammonium salts and monoamine salts; andcombinations thereof. Preferred cation sources are compounds ofmagnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals. The amount of cation used in the composition is readilydetermined based on desired level of neutralization. As discussed above,for HNP compositions, the acid groups are neutralized to 70% or greater,preferably 70 to 100%, more preferably 90 to 100%. In one embodiment, anexcess amount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In other embodiments,partially-neutralized compositions are prepared, wherein 10% or greater,normally 30% or greater of the acid groups are neutralized. Whenaluminum is used as the cation source, it is preferably used at lowlevels with another cation such as zinc, sodium, or lithium, sincealuminum has a dramatic effect on melt flow reduction and cannot be usedalone at high levels. For example, aluminum is used to neutralize about10% of the acid groups and sodium is added to neutralize an additional90% of the acid groups.

In a particular embodiment, the core includes at least one additionalthermoplastic intermediate core layer formed from a compositioncomprising an ionomer selected from DuPont® HPF ESX 367, HPF 1000, HPF2000, HPF AD1035, HPF AD1035 Soft, HPF AD1040, and AD1172 ionomers,commercially available from E. I. du Pont de Nemours and Company. Thecoefficient of restitution (“COR”), compression, and surface hardness ofeach of these materials, as measured on 1.55″ injection molded spheresaged two weeks at 23° C./50% RH, are given in Table 1 below.

TABLE 1 Solid Sphere Solid Sphere Solid Sphere Shore D Example CORCompression Surface Hardness HPF 1000 0.830 115 54 HPF 2000 0.860 90 47HPF AD1035 0.820 63 42 HPF AD1035 Soft 0.780 33 35 HPF AD 1040 0.855 13560 HPF AD1172 0.800 32 37

In another particular embodiment, the core includes at least oneadditional thermoplastic intermediate core layer formed from a blend oftwo or more ionomers. In a particular aspect of this embodiment, theblend is a 50 wt %/50 wt % blend of two different partially-neutralizedethylene/methacrylic acid copolymers.

In another particular embodiment, the core includes at least oneadditional thermoplastic intermediate core layer formed from a blend ofone or more ionomers and a maleic anhydride-grafted non-ionomericpolymer. In a particular aspect of this embodiment, the non-ionomericpolymer is a metallocene-catalyzed polymer. In another particular aspectof this embodiment, the blend includes a partially-neutralizedethylene/methacrylic acid copolymer and a maleic anhydride-graftedmetallocene-catalyzed polyethylene.

In yet another particular embodiment, the core includes at least oneadditional thermoplastic intermediate core layer formed from acomposition selected from the group consisting of partially- andfully-neutralized ionomers optionally blended with a maleicanhydride-grafted non-ionomeric polymer; polyester elastomers; polyamideelastomers; and combinations of two or more thereof.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin. Such ionicplasticizers are used to make conventional ionomer composition moreprocessable as described in Rajagopalan et al., U.S. Pat. No. 6,756,436,the disclosure of which is hereby incorporated by reference. In thepresent invention such ionic plasticizers are optional. In one preferredembodiment, a thermoplastic ionomer composition is made by neutralizingabout 70 wt % or more of the acid groups without the use of any ionicplasticizer. On the other hand, in some instances, it may be desirableto add a small amount of ionic plasticizer, provided that it does notadversely affect the heat-resistance properties of the composition. Forexample, the ionic plasticizer may be added in an amount of about 10 toabout 50 weight percent (wt. %) of the composition, more preferably 30to 55 wt. %.

The organic acids may be aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. Suitable fatty acid saltsinclude, for example, metal stearates, laureates, oleates, palmitates,pelargonates, and the like. For example, fatty acid salts such as zincstearate, calcium stearate, magnesium stearate, barium stearate, and thelike can be used. The salts of fatty acids are generally fatty acidsneutralized with metal ions. The metal cation salts provide the cationscapable of neutralizing (at varying levels) the carboxylic acid groupsof the fatty acids. Examples include the sulfate, carbonate, acetate andhydroxide salts of metals such as barium, lithium, sodium, zinc,bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, and blends thereof. It is preferred the organic acids and saltsbe relatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

Other suitable thermoplastic polymers that may be used to form the innercover layer include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof.): (a)polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (b) polyamides, polyamide-ethers, andpolyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,6,001,930, and 5,981,654, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof; (c)polyurethanes, polyureas, polyurethane-polyurea hybrids, and blends oftwo or more thereof; (d) fluoropolymers, such as those disclosed in U.S.Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (e) polystyrenes, such as poly(styrene-co-maleicanhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate),polyethylene styrene, and blends of two or more thereof; (f) polyvinylchlorides and grafted polyvinyl chlorides, and blends of two or morethereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the outer core and/or inner cover layers inaccordance with this invention. For example, thermoplastic polyolefinssuch as linear low density polyethylene (LLDPE), low densitypolyethylene (LDPE), and high density polyethylene (HDPE) may becross-linked to form bonds between the polymer chains. The cross-linkedthermoplastic material typically has improved physical properties andstrength over non-cross-linked thermoplastics, particularly attemperatures above the crystalline melting point. Preferably a partiallyor fully-neutralized ionomer, as described above, is covalentlycross-linked to render it into a thermoset composition (that is, itcontains at least some level of covalent, irreversable cross-links).Thermoplastic polyurethanes and polyureas also may be converted intothermoset materials in accordance with the present invention.

Modifications in the thermoplastic polymeric structure of thermoplasticscan be induced by a number of methods, including exposing thethermoplastic material to high-energy radiation or through a chemicalprocess using peroxide. Radiation sources include, but are not limitedto, gamma-rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms andallows for considerable depth of treatment, if necessary. For corelayers requiring lower depth of penetration, electron-beam acceleratorsor UV and IR light sources can be used. Useful UV and IR irradiationmethods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, whichare incorporated herein by reference. The thermoplastic core layers maybe irradiated at dosages greater than 0.05 Mrd, preferably ranging from1 Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and mostpreferably from 4 Mrd to 10 Mrd. In one preferred embodiment, the coresare irradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered structure comprising an inner core andouter core layer. The hardness of the core sub-assembly (inner core andouter core layer) is an important property. In general, cores withrelatively high hardness values have higher compression and tend to havegood durability and resiliency. However, some high compression balls arestiff and this may have a detrimental effect on shot control andplacement. Thus, the optimum balance of hardness in the coresub-assembly needs to be attained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the outer core layer has a greater hardness value thanthe inner surface of the outer core layer, the given outer core layerwill be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the outer core layer has a lesser hardness valuethan the inner surface of the outer core layer, the given outer corelayer will be considered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The hardness gradients of the inner core are discussed above. On theother hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or63 or 65 or 67 or 720 or 72 or 73 or 76 Shore C, and an upper limit ofabout 78 or 80 or 84 or 87 or 88 or 89 or 90 or 92 or 95 Shore C. And,the inner surface of the outer core layer (H_(inner surface of OC)) ormidpoint hardness of the outer core layer (H_(midpoint of OC)),preferably has a hardness of about 40 Shore D or greater, and morepreferably within a range having a lower limit of about 40 or 42 or 44or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or 60or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90 ShoreD. The inner surface hardness (H_(inner surface of OC)) or midpointhardness (H_(midpoint of OC)) of the outer core layer, as measured inShore C units, preferably has a lower limit of about 40 or 42 or 44 or45 or 47 or 50 or 52 or 54 or 55 or 58 or 60 or 63 or 65 or 67 or 70 or73 or 75 Shore C, and an upper limit of about 78 or 80 or 85 or 88 or 89or 90 or 92 or 95 Shore C. The midpoint of the outer core layer is takenat a point equidistant from the inner surface and outer surface of thelayer to be measured. Once one or more core layers surround a layer ofinterest, the exact midpoint may be difficult to determine, therefore,for the purposes of the present invention, the measurement of “midpoint”hardness of a layer is taken within plus or minus 1 mm of the measuredmidpoint of the layer.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is less than the outer surface hardness(H_(inner core surface)) or midpoint hardness (H_(midpoint of OC)), ofthe inner core by at least 3 Shore C units and more preferably by atleast 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the inner core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

As discussed above, the inner core is preferably formed from a foamedthermoplastic or thermoset composition and more preferably foamedpolyurethanes. And, the outer core layer is formed preferably from anon-foamed thermoset composition such as polybutadiene rubber. The outercore layer also may be formed from non-foamed thermoplasticcompositions.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 10 Shore C to about 60 Shore C, preferably about 13 Shore C toabout 55 Shore C; and the (H_(outer surface of OC)) is in the range ofabout 65 to about 96 Shore C, preferably about 68 Shore C to about 94Shore C or about 75 Shore C to about 93 Shore C, to provide a positivehardness gradient across the core assembly. The gradient across the coreassembly will vary based on several factors including, but not limitedto, the dimensions of the inner core, optional intermediate core layer,and outer core layers.

As discussed above, in one preferred embodiment, the inner core has aspecific gravity in the range of about 0.25 to about 1.50 g/cc. Also, asdiscussed above, the specific gravity of the inner core may vary atdifferent points of the inner core structure. That is, there may be aspecific gravity gradient in the inner core. For example, in onepreferred version, the geometric center of the inner core has a densityin the range of about 0.25 to about 0.75 g/cc; while the outer skin ofthe inner core has a density in the range of about 0.75 to about 1.50g/cc.

Meanwhile, the outer core layer preferably has a relatively highspecific gravity. Thus, the specific gravity of the inner core layer(SG_(inner)) is preferably less than the specific gravity of the outercore layer (SG_(outer)). By the term, “specific gravity of the outercore layer” (“SG_(outer)”), it is generally meant the specific gravityof the outer core layer as measured at any point of the outer corelayer. The specific gravity values at different points in the outer corelayer may vary. That is, there may be specific gravity gradients in theouter core layer similar to the inner core. For example, the outer corelayer may have a specific gravity within a range having a lower limit ofabout 0.50 or 0.60 or 0.70 or 0.75 or 0.85 or 0.95 or 1.00 or 1.10 or1.25 or 1.30 or 1.36 or 1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or1.75 or 2.00 and an upper limit of 2.50 or 2.60 or 2.80 or 2.90 or 3.00or 3.10 or 3.25 or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 5.00 or 5.10 or5.20 or 5.30 or 5.40 or 6.00 or 6.20 or 6.25 or 6.30 or 6.40 or 6.50 or7.00 or 7.10 or 7.25 or 7.50 or 7.60 or 7.65 or 7.80 or 8.00 or 8.20 or8.50 or 9.00 or 9.75 or 10.00 g/cc.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center (the center piece(for example, inner core) has a higher specific gravity than the outerpiece (for example, outer core layers), less force is required to changeits rotational rate, and the ball has a relatively low Moment ofInertia. In such balls, most of the mass is located close to the ball'saxis of rotation and less force is needed to generate spin. Thus, theball has a generally high spin rate as the ball leaves the club's faceafter making impact. Conversely, if the ball's mass is concentratedtowards the outer surface (the outer piece (for example, outer corelayers) has a higher specific gravity than the center piece (forexample, inner core), more force is required to change its rotationalrate, and the ball has a relatively high Moment of Inertia. That is, insuch balls, most of the mass is located away from the ball's axis ofrotation and more force is needed to generate spin. Such balls have agenerally low spin rate as the ball leaves the club's face after makingimpact.

More particularly, as described in Sullivan, U.S. Pat. No. 6,494,795 andLadd et al., U.S. Pat. No. 7,651,415, the formula for the Moment ofInertia for a sphere through any diameter is given in the CRC StandardMathematical Tables, 24th Edition, 1976 at 20 (hereinafter CRCreference). The term, “specific gravity” as used herein, has itsordinary and customary meaning, that is, the ratio of the density of asubstance to the density of water at 4° C., and the density of water atthis temperature is 1 g/cm³.

In one embodiment, the golf balls of this invention are relatively lowspin and long distance. That is, the foam core construction, asdescribed above, wherein the inner core is made of a foamed compositionhelps provide a relatively low spin ball having good resiliency. Theinner foam cores of this invention preferably have a Coefficient ofRestitution (COR) of about 0.300 or greater; more preferably about 0.400or greater, and even more preferably about 0.450 or greater. Theresulting balls containing the dual-layered core constructions of thisinvention and cover of at least one layer preferably have a COR of about0.700 or greater, more preferably about 0.730 or greater; and even morepreferably about 0.750 to 0.810 or greater. The inner foam corespreferably have a Soft Center Deflection Index (“SCDI”) compression, asdescribed in the Test Methods below, in the range of about 50 to about190, and more preferably in the range of about 60 to about 170.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 38 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a cover which may be multi-layeredand in addition may contain intermediate (casing) layers, and thethickness levels of these layers also must be considered. Thus, ingeneral, the dual-layer core structure normally has an overall diameterwithin a range having a lower limit of about 1.00 or 1.20 or 1.30 or1.40 inches and an upper limit of about 1.58 or 1.60 or 1.62 or 1.66inches, and more preferably in the range of about 1.3 to 1.65 inches. Inone embodiment, the diameter of the core sub-assembly is in the range ofabout 1.45 to about 1.62 inches.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball sub-assembly includes the core structure and one or morecasing (mantle) layers disposed about the core. In one particularlypreferred version, the golf ball includes a multi-layered covercomprising inner and outer cover layers. The inner cover layer ispreferably formed from a composition comprising an ionomer or a blend oftwo or more ionomers that helps impart hardness to the ball. In aparticular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont). Fusabond 525D® is a maleic anhydride-grafted,metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt %maleic anhydride grafted onto the copolymer. A particularly preferredblend of high acid ionomer and maleic anhydride-grafted polymer is an 84wt %/16 wt % blend of Surlyn 8150® and Fusabond 525D®. Blends of highacid ionomers with maleic anhydride-grafted polymers are furtherdisclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, theentire disclosures of which are hereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make the casing (mantle) and cover layers maycontain a wide variety of fillers and additives to impart specificproperties to the ball. For example, relatively heavy-weight andlight-weight metal fillers such as, particulate; powders; flakes; andfibers of copper, steel, brass, tungsten, titanium, aluminum, magnesium,molybdenum, cobalt, nickel, iron, lead, tin, zinc, barium, bismuth,bronze, silver, gold, and platinum, and alloys and combinations thereofmay be used to adjust the specific gravity of the ball. Other additivesand fillers include, but are not limited to, optical brighteners,coloring agents, fluorescent agents, whitening agents, UV absorbers,light stabilizers, surfactants, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, clay, mica, talc, glass flakes,milled glass, and mixtures thereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the intermediate layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

A single cover or, preferably, an inner cover layer is formed around theouter core layer. When an inner cover layer is present, an outer coverlayer is formed over the inner cover layer. Most preferably, the innercover is formed from an ionomeric material and the outer cover layer isformed from a polyurethane material, and the outer cover layer has ahardness that is less than that of the inner cover layer. Preferably,the inner cover has a hardness of greater than about 60 Shore D and theouter cover layer has a hardness of less than about 60 Shore D. In analternative embodiment, the inner cover layer is comprised of apartially or fully neutralized ionomer, a thermoplastic polyesterelastomer such as Hytrel™, commercially available form DuPont, athermoplastic polyether block amide, such as Pebax™, commerciallyavailable from Arkema, Inc., or a thermoplastic or thermosettingpolyurethane or polyurea, and the outer cover layer is comprised of anionomeric material. In this alternative embodiment, the inner coverlayer has a hardness of less than about 60 Shore D and the outer coverlayer has a hardness of greater than about 55 Shore D and the innercover layer hardness is less than the outer cover layer hardness.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Manufacturing of Golf Balls

As described above, the inner core preferably is formed by molding afoamed composition. The outer core layer, which surrounds the innercore, is formed by molding a composition over the inner core. Then, thecasing and/or cover layers are applied over the core sub-assembly. Priorto this step, the core structure may be surface-treated to increase theadhesion between its outer surface and the next layer that will beapplied over the core. Such surface-treatment may include mechanicallyor chemically-abrading the outer surface of the core. For example, thecore may be subjected to corona-discharge, plasma-treatment,silane-dipping, or other treatment methods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any casing layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the core sub-assembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the sub-assembly.In another method, the ionomer composition is injection-molded directlyonto the core sub-assembly using retractable pin injection molding. Anouter cover layer comprising a polyurethane or polyurea composition overthe ball sub-assembly may be formed by using a casting process.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball. In FIG. 6, a finished golf ball(38) having a dimpled outer cover (40) made in accordance with thepresent invention is shown. As discussed above, various patterns andgeometric shapes of the dimples (40) can be used to modify theaerodynamic properties of the golf ball.

Different ball constructions can be made using the methods and coreconstructions of this invention as shown in FIGS. 1-6. Such golf ballconstructions include, for example, five-piece, and six-piececonstructions. It should be understood that the golf ball components andfinished golf balls shown in FIGS. 1-6 are for illustrative purposesonly, and they are not meant to be restrictive. Other golf ballconstructions can be made in accordance with this invention. Forexample, the foam composition of this invention is primarily discussedherein as being suitable for producing a foam inner core or center for agolf ball. However, it is recognized that this foam composition may beused for producing an outer core layer, casing layer, cover, or anyother suitable component layer for the golf ball in accordance with thisinvention.

Cores Having Three Layers

In another example, multi-layered cores having an inner core,intermediate core layer, and outer core layer, wherein the intermediatecore layer is disposed between the intermediate and outer core layersmay be prepared in accordance with this invention. More particularly, asdiscussed above, the inner core may be constructed from a foamedcomposition, preferably foamed polyurethane. Meanwhile, the intermediateand outer core layers may be formed from non-foamed thermoset orthermoplastic materials. Suitable thermoset and thermoplasticcompositions that may be used to form the intermediate/outer core layersare discussed above. For example, each of the intermediate and outercore layers may be formed from a thermoset rubber composition. Thus, theintermediate core layer may be formed from a first thermoset rubbercomposition; and the outer core layer may be formed from a secondthermoset rubber composition. In another embodiment, the intermediatecore layer is formed from a non-foamed thermoset composition; and theouter core layer is formed from a non-foamed thermoplastic composition.In a third embodiment, the intermediate core layer is formed from anon-foamed thermoplastic composition; and the outer core layer is formedfrom a non-foamed thermoset composition. Finally, in a fourthembodiment, the intermediate core layer is formed from a firstnon-foamed thermoplastic composition; and the outer core layer is formedfrom a second non-foamed thermoplastic compositions.

The above-discussed thermoset and thermoplastic compositions may be usedto form the intermediate and outer core layers. In one embodiment, thespecific gravity of the inner core (foamed composition) is less than thespecific gravity of the intermediate and outer core layers. The specificgravities of the intermediate and outer core layers may be the same ordifferent. In one version, the specific gravity of the intermediate corelayer is greater than the specific gravity of the outer core layer. Inanother version, the specific gravity of the outer core is greater thanthe specific gravity of the intermediate core layer.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used. Likewise,the midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. Once again, when one or more core layerssurround a layer of interest, the exact midpoint may be difficult todetermine, therefore, for the purposes of the present invention, themeasurement of “midpoint” hardness of a layer is taken within plus orminus 1 mm of the measured midpoint of the layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Density.

The density refers to the weight per unit volume (typically, g/cm³) ofthe material and can be measured per ASTM D-1622.

Examples

The following prophetic examples describe core assemblies that can bemade in accordance with this invention. The foam center of the core canbe made from a polyurethane or ethylene vinyl acetate foam or any othersuitable foam formulation. The outer core layer can be made from anysuitable thermoset or thermoplastic composition. For example,polybutadiene rubbers can be used. The properties of the core assembliesare described in below Table 2.

TABLE 2 Examples A B C D E Inner Core Material type foamed foamed foamedfoamed foamed polyurethane ethylene polyurethane polyurethane ethylenevinyl acetate vinyl acetate Diameter  0.3″ 0.75″    1″ 0.75″    1″Volume (cm³) 0.23 3.62 8.6 3.62 8.6 Density 0.5 0.5 0.7 0.6 0.7H_(inner core center) 12 C 24 C 23 C 20 C 40 CH_(midpoint IC outer region) 15 C 30 C 26 C 24 C 48 CH_(inner core surface) 16 C 33 C 29 C 25 C 51 C Inner Core gradient +4+9 +6 +5 +11 Outer Core Layer Material type thermoset thermoplasticthermoplastic thermoset thermoset rubber polymer polymer rubber rubberThickness 0.635″  0.40″ 0.275″ 0.40″ 0.285″ Core volume (cm³) 33.2 31.931.9 31.9 33.2 Outer core volume (cm³) 33 28.3 23.3 28.3 24.6 CoreAssembly Diameter 1.57″ 1.55″  1.55″ 1.55″  1.57″ Density 1.16 1.24 1.331.18 1.31 H_(outer surface OC) 81 C 78 C 85 C 85 C 89 C Core Gradient+69 +54 +62 +65 +49

It is understood that the golf ball compositions, constructions, andproducts described and illustrated herein represent only someembodiments of the invention. It is appreciated by those skilled in theart that various changes and additions can be made to compositions,constructions, and products without departing from the spirit and scopeof this invention. It is intended that all such embodiments be coveredby the appended claims.

We claim:
 1. A golf ball, comprising: i) an inner core comprising a foamcomposition having a geometric center, an outer region, and outersurface, wherein the foam composition is foamed in the center and atleast partially-collapsed in the outer region, the inner core having adiameter in the range of about 0.100 to about 1.100 inches and an outersurface hardness (H_(inner core surface)) and a center hardness(H_(inner core center)), the H_(inner core surface) being greater thanthe H_(inner core center) to provide a positive hardness gradient in theinner core; ii) an outer core layer comprising a non-foamed thermoset orthermoplastic composition, the outer core layer being disposed about theinner core layer and having a thickness in the range of about 0.100 toabout 0.750 inches, and an outer surface hardness(H_(outer surface of OC)), wherein the (H_(outer surface of OC)) isgreater than the (H_(inner core center)) to provide a positive hardnessgradient across the core assembly; and iii) a cover layer comprising athermoset or thermoplastic material, the cover layer having a thicknessin the range of about 0.010 to about 0.080 inches, wherein anintermediate layer is disposed between the cover layer and outer corelayer.
 2. The golf ball of claim 1, wherein the cover layer comprises amaterial selected from the group consisting of polyurethanes, polyureas,and hybrids, copolymers, and blends thereof.
 3. The golf ball of claim1, wherein the cover layer comprises an ethylene acid copolymer ionomermaterial.
 4. The golf ball of claim 1, wherein the cover has a materialhardness in the range of about 70 to about 92 Shore C.
 5. The golf ballof claim 1, wherein the inner core comprises a foamed polyurethanecomposition.
 6. The golf ball of claim 1, wherein the inner corecomprises a foamed ethylene vinyl acetate composition.
 7. The golf ballof claim 1, wherein the outer core layer comprises a thermosetpolybutadiene rubber composition.
 8. The golf ball of claim 1, whereinthe H_(inner core center) is in the range of about 10 to about 55 ShoreC and the H_(inner core surface) is in the range of about 15 to about 60Shore C to provide a positive hardness gradient.
 9. The golf ball ofclaim 1, wherein the inner core further has a midpoint hardness in theouter region (H_(midpoint inner core outer region)) and theH_(inner core surface) is greater than theH_(midpoint inner core outer region) and theH_(midpoint inner core outer region) is greater than theH_(inner core center).
 10. The golf ball of claim 1, wherein the outercore layer has an outer surface hardness (H_(outer surface of OC)) and amidpoint hardness (H_(midpoint of OC)), the H_(outer surface of OC)being greater than the (H_(midpoint of OC)), to provide a positivehardness gradient.
 11. The golf ball of claim 10, wherein theH_(midpoint of OC) is in the range of about 45 to about 90 Shore C andthe H_(outer surface of OC) is in the range of about 50 to about 98Shore C.